One technique for improving availability of applications in case hardware failure occurs is a technique in which an HA (High Availability) configuration is adopted in a storage subsystem. Patent Literature 1 discloses providing a same virtual volume ID to two real volumes, a first real volume of a first storage subsystem and a second real volume of a second storage subsystem connected to the first storage subsystem, such that one virtual volume is provided to a host computer, wherein if the host computer writes data to the first real volume, the first storage subsystem writes data to the first real volume and also transfers the data to the second storage subsystem, and the second storage subsystem writes the received data to the second real volume, by which the HA configuration is realized.
On the other hand, the improvement of performance of the host computer has enabled a virtual host computer (Virtual Machine: VM) to operate on a physical host computer. Further, a technique (Distributed Resource Scheduler) for changing the host computer on which the VM operates among host computers is known (refer for example to Non-Patent Literature 1).